1. Field of the Invention
The invention relates to a scroll compressor used, for instance, in an air conditioning machine or a refrigerator.
2. Description of the Related Art
FIG. 19 is a cross sectional view of the conventional scroll compressor which is disclosed in laid-open patent publication No. 3-237286. In FIG. 19, numeral 1 denotes a fixed scroll which has a wrap portion, 2, a discharge outlet formed almost at the center of the fixed scroll 1, 22, a discharge valve, 3, an orbital scroll having wrap members, 4, an Oldham ring which prevents the rotation of the orbital scroll 3 and gives moving motion to the orbital scroll 3, 5, a thrust bearing which receives thrust load from the orbital scroll 3, 6, a crank shaft which transfers the driving force from the electric motor to the orbital scroll 3, 6a, an eccentric pin installed at the top edge of the crank shaft 6, 21, a driving bush which transfers the rotational force of the crank shaft 6 to the orbital scroll 3 as an eccentric rotational force, 7, a centrifugal pump hole which is formed eccentrically in the crank shaft 6, 8, a main frame which supports the Oldham ring 4 and the thrust bearing 5, 9, a sub-frame, 10, a balance weight, respectively. The components shown in above-mentioned reference codes 1-10 comprise a compression element of the scroll compressor. Numeral 11 denotes a stator, 12, a rotor, respectively. These components 11 and 12 comprise an element of the electric motor.
The fixed scroll 1 in the compression element, the main frame 8 and the sub-frame 9 are fitted airtightly by such as shrink fit to the inside wall of a sealed shell 13. Thereby, a discharge muffler 14 and a suction pressure chamber 15, i.e. a suction pressure ambient atmosphere portion, are divided along the longitudinal direction. Furthermore, numeral 16 denotes a discharge pipe for discharging refrigerant gas, 17, a suction pipe for introducing the refrigerant gas, 18, a lubricating oil for providing it to the lubrication portion such as the compression bearing, respectively.
An operation of the aforementioned conventional scroll compressor is subsequently described. The force generated by the electric motor is transferred to the orbital scroll 3 through the crank shaft 6. The generated force causes the volume of the compression chamber 19 which is formed between a pair of the wrap members (protruded portions) of the fixed scroll 1 and the orbital scroll 3 to vary. Thereby, the compression chamber 19 intakes and compresses the refrigerant gas which flows toward inside from outside of the wrap members via the suction path 20 from the suction pipe 17. The compressed refrigerant gas is discharged from the discharge outlet 2 into the discharge muffler 14 and then discharged via the discharge pipe 16 to the outside of the compressor.
An oil feeding head is applied to a lubricating oil 18 at the bottom of the sealed shell 13 by the centrifugal force through the eccentric hole 7 of the crank shaft 6. The lubricating oil 18 goes up along the inside of the hole 7 and lubricates the sliding portion of the bearing, then is drained into the suction pressure chamber 15 and returns to the bottom of the sealed shell 13.
The orbital motion of orbital scroll 3 is permitted between the orbital scroll 3 and main frame 8, but the rotation of the orbital scroll 3 which rotates about its own axis is prevented by arranging the Oldham ring 4.
The function of the Oldham ring 4 is explained using FIG. 20. The Oldham ring 4 defines a doughnut shape. On the Oldham ring 4, a pair of protruding first keys 4b are formed on the bottom surface of the Oldham ring 4 and face an upper surface of the main frame 8, and a pair of second protruding keys 4a are formed on an upper surface and face a bottom surface of the orbital scroll 3. The first keys 4b and the second keys 4a are arranged perpendicularly each other. The key grooves 8a corresponding to the first keys 4b are formed on the upper surface of the main frame 8 and the key grooves 3a corresponding to the second keys 4a are formed on the back of the orbital scroll 3. Thereby, the Oldham ring 4 moves reciprocally for each groove, and therefore the rotation of the orbital scroll 3 is prevented.
FIG. 21 is a main cross sectional view as seen from the axis direction which shows a compression mechanism of the conventional scroll compressor. In FIG. 21, the orbital scroll 3 is engaged to the fixed scroll 1 at the position of a transversal direction separated by 180 degrees of the wrap phase by using the Oldham ring 4. The orbital scroll 3 is enforced by the eccentric rotating motion having a predetermined distance by the eccentric pin 6a located at the top edge of the crank shaft 6 and the driving bush 21 attached thereon. Respective volumes of a plurality of closed spaces (compression chambers) are decreased and compressed by the eccentric rotating motion of the orbital scroll 3. Where, O1 denotes a center of the fixed scroll 1 and O2 denotes a center of the orbital scroll 3. The distance between O1 and O2 denotes an orbital radius r.sub.0 of the orbital scroll 3. In FIG. 21, the points where the fixed scroll 1 contacts the orbital scroll 3 are indicated by A1, A2, A3, A4, A5, A6. The closed spaces (compression chambers) are partitioned by these points.
The moment acting on the Oldham ring 4 is described using FIG. 22. FIG. 22 is an illustration which shows a rotational moment acting on the orbital scroll 3 at the normal operation of the conventional scroll compressor. The Oldham ring 4 prevents the rotation of the orbital scroll 3. A moment which causes the orbital scroll 3 to rotate around its own axis is generated by the reactive force which is generated against the force for compressing the refrigerant.
The reactive force F.theta. against the force which is necessary to compress the refrigerant is directed toward the reverse rotational direction around the principal axis O.sub.1 (or around the center point of the fixed scroll 1). The point of action corresponds to a middle point on the straight line between the principal axis center O.sub.1 and the center O.sub.2 of the driving bush 21 (or at the center of the orbital scroll 3) is shown in FIG. 24.
When this force F.theta. is watched from driving bush 21 center O.sub.2 (or at the center of the orbital scroll 3), the orbital scroll 3 receives the rotational moment M toward the same rotational direction as that of the principal axis 6. Accordingly, the keys 4a and 4b of the Oldham ring 4 are to receive the load at the surfaces which denies this rotational direction. The numeral 30 in FIG. 22 indicates portions where the Oldham ring key grooves usually receive this load and the orbital surfaces of the Oldham ring keys and the key grooves are formed at normal operation.
The fixed scroll 1 and the orbital scroll 3 continue the compressing operation using this Oldham ring 4 in keeping the relative phase difference of 180 degrees.
FIG. 23 is a cross sectional view which shows an enlarged Oldham key and a key groove of the conventional scroll compressor. In general, the clearance .epsilon. between the Oldham ring key and key groove is defined as a sliding surface fitting clearance which is set within the range of the desired dimensional tolerance at machining. This clearance .epsilon. is very strictly controlled to be as small as possible.
At a normal operation, if the clearance .epsilon. between the key and key groove in this sliding surface becomes large, the phase difference between the fixed scroll 1 and the orbital scroll 3 becomes large. If there arises the larger phase difference between the two wrap members, the clearance is formed between the wrap side surfaces and the airtightness of the compression chamber is ruined. As a result, the performance of the scroll compressor will largely deteriorate.
The variable crank mechanism using the driving bush 21 is described in FIG. 24. FIG. 24 is a main cross sectional view of the variable crank mechanism.
In order to seal the clearance, toward the radius direction, of wrap side surfaces of the scroll compressor, a crank having a variable orbital radius r.sub.0 (or the orbital radius of orbital scroll 3) is used. In FIG. 24, O.sub.1 is a rotating center of the principal axis, O.sub.2 is a center of the driving bush 21. The driving bush 21 is installed on the eccentric pin 6a which is located at the top edge of the crank shaft 6. When the scroll compressor starts its operation, the reactive force F.theta. and the radius direction force Fr (mainly centrifugal force) act to the center of the driving bush 21. The reactive force F.theta. is against the force which compresses the refrigerant toward the center of the driving bush 21. The radius direction force Fr causes the crank radius O1.about.O2 (or the orbital radius r.sub.0 of the orbital scroll 3) to increase, and causes the clearance between the wrap side surfaces to be zero automatically. As a result, the wrap side walls mutually push and touch as shown in A1.about.A6 of FIG. 21. Accordingly, the performance of the scroll compressor can be increased by this sealing effect.
In case of the conventional scroll compressor, at a stopping state of the compressor, especially when the compressor has been stopping for a long time and the temperature of the refrigerant is low, the refrigerant stored inside the refrigerating or the air conditioning equipment liquefies and abundantly flows into the inside of the compressor. In this case, the compressor shell and/or the suction path is filled with a lot of saturated liquid which abundantly dissolves the lubricating oil inside the compressor shell.
If the compressor is started in such a state, the space in which the saturated liquid stays is the same as that of the suction pressure space. Accordingly, at starting of the compressor, the refrigerant of saturated liquid is vaporized suddenly by the sudden pressure reduction changed from a balance state of pressure. The refrigerant of the saturated liquid becomes into a foam state according to the sudden pressure reduction and viscosity of lubricating oil.
Bubbles formed by the refrigerant and the lubricating oil are introduced into the compression chamber via the suction path 20. In this case, the pressure value which is generated inside the closed compression chamber becomes from several to several tens of times in comparison with the pressure value when the refrigerant is compressed under the normal operation. If such an abnormally high pressure is repeated, the wrap members formed by the comparatively thin shape break down without overcoming the pressure in the worst case. Even if the wrap members do not break down, the compression load according to the liquid compression suddenly increases. As a result, the driving torque of the electric motor falls behind the torque which compresses liquid refrigerant and a problem of the starting failure has been brought about.
Furthermore, when the liquid refrigerant containing a large quantity of lubricating oil is compressed and discharged out of the compressor, a quantity of the lubricating oil in the compressor decreases. As a result, an abnormal abrasion and a seizure of the sliding portion are caused by the feeding failure of the lubricating oil into the sliding portion of the compressor.